Rostrum and support structure for a rostrum

ABSTRACT

In a first aspect, a rostrum support structure for a rostrum comprises a pair of frame units which are inclined towards one another, extending from floor contacting portions to rostrum support points, truss members being provided extending downwardly and inwardly from the first frame members towards a linking member or towards the other frame member, to provide a triangulated structure. 
     In a second aspect, a rostrum structure comprises a first rostrum unit and a second rostrum unit, a latch being provided for fixing the second rostrum unit with respect to the first rostrum unit in an extended position, the latch comprising a movable member mounted on one of the first and second rostrum units and a latch surface mounted on the other of the first and second rostrum units, the movable member being movable into and out of engagement with the latch surface, preferably by rotation, in a direction parallel to the planes of the decks and substantially normal to the retraction direction.

This invention relates to a support structure for a rostrum and to a rostrum.

The present invention is particularly concerned with a rostrum, or a support structure therefor, in which a plurality of decks are received upon respective rostrum support structures, the rostrum support structures and, preferably, the decks with them, being retractable together, so that, when not in use, the rostrum can be stored in a much smaller space than would be represented by the rostrum in its position in use.

A rostrum of this type is described in International Patent Application No. WO2008/149077. This provides a support structure for a rostrum, comprising a first A frame and at least a second A frame which is nestable and retractable into the first A frame. This provides a support structure which is inherently stable in the extended position, without relying upon the decks to provide further support or increased rigidity. It distributes the load across a large floor surface area.

Although this structure is rigid and reliable, the inventor has realised that there is a need for a support structure for a rostrum, which has a smaller number of points contacting the floor but which is still strong and rigid. The inventor has realised that, whereas the invention of WO2008/149077 typically employs two support structures to support each individual deck, the support structures being only connected to one another through the respective deck, a simpler, more compact structure requiring a smaller number of ground contacting points can be provided if each deck is supported by at least two separate deck supports which are supported by a single structure. To achieve this, the inventor has realised that each support point needs to be provided with a respective frame member and a truss, the trusses connecting to the opposite frame member or to a linking member which links the frame members.

Accordingly, in a first aspect, the present invention provides a support structure for a rostrum, comprising:

-   -   a first frame unit and at least a second frame unit, retractable         into the     -   first frame unit,     -   each frame unit comprising:     -   a first frame member, extending from a floor contacting part to         a first rostrum support point and a first truss extending from         the first frame member,     -   a second frame member, extending from a floor contacting part to         a second rostrum support point and a second truss extending from         the second frame member,     -   wherein, in each frame unit:     -   (a) there is a linking member, connecting the first and second         frame members and first and second trusses, at points displaced         from the first and second rostrum support points; or     -   (b) the first and second trusses are connected to the second and         first frame members respectively, at points displaced from the         first and second rostrum support points.

According to the first aspect of the invention, a strong, rigid structure can be provided which can support a deck of a rostrum at two separate points, allowing a rigid, compact, stackable structure to be formed.

The present inventor has further realised that, when a rostrum is formed from a plurality of stackable structures, in the extended position (ready for use) the individual rostrum units with their respective decks need to be securely fixed with respect to one another so that they do not inadvertently stack when people are trying to use the rostrum. For this purpose, a latching structure may be provided. The present inventor has realised, that, whereas it has been known in the past to provide a latching structure in which a latch moves behind a latching surface, moving in a direction which is normal to the decks and to the retraction direction, there is sometimes insufficient space between adjacent decks to contain the range of vertical movement implied, to provide a sufficiently positive latching between rostrum units. The inventor has realised that a more compact structure can be provided, in which the latch moves into and out of engagement with a respective latching surface in a direction which is parallel to the plane of the decks and substantially normal to the retraction direction.

Accordingly, in a second aspect, the present invention provides a rostrum structure, comprising:

-   -   a first rostrum unit and at least a second rostrum unit, wherein         the second rostrum unit is movable in a retraction direction         between an extended position and a position in which it is         retracted into the first rostrum unit, each rostrum unit having         a deck;     -   a latch, for fixing the second rostrum unit with respect to the         first rostrum unit in the extended position, the latch         comprising a movable member, mounted on one of the first and         second rostrum units, and a latch surface mounted on the other         of the first and second rostrum units, with which the movable         member engages to fix the second rostrum unit with respect to         the first rostrum unit in the extended position, the movable         member being movable into and out of engagement with the latch         surface in a direction which is substantially parallel to the         planes of the decks and substantially normal to the retraction         direction.

The first aspect of the present invention further provides a rostrum, comprising a plurality of decks supported by a plurality of rostrum support structures according to the first aspect of the invention. The rostrum of the first aspect of the invention may incorporate the features of the second aspect of the invention.

Preferred and optional features will be described below.

In the support structure of the first aspect of the invention there are at least two frame units, but there may be more than two frame units, for example 5 units or more, possibly 10 units or more. Where there are a plurality of frame units, there is a largest frame unit and a smallest frame unit, the plurality of frame units forming a set of frame units each frame unit apart from the largest being retractable and nestable into a larger frame unit, and all frame units except the smallest frame unit being capable of receiving a smaller frame unit retracted thereinto.

A larger frame unit, for example the first frame unit, preferably defines an internal shape and a smaller frame unit (for example the second frame unit) defines an outer frame shape which is geometrically similar to and slightly smaller than the internal shape of the larger frame unit.

The first and second frame units and, suitably, the first and second trusses preferably all lie within a single plane. Preferably, when in use, the plane is aligned in a vertical direction.

Where there is a linking member, linking the first and second frame members and the first and second trusses, the linking member is suitably located in a plane which is displaced from the plane which includes the first frame member, second frame member, first truss and second truss. In this way, an uninterrupted space can be defined inside the first frame member, second frame member, first truss and second truss for receiving the corresponding units of another frame unit, unobstructed by the linking member. The linking members of respective frame units are preferably located so that they do not come into contact with one another. For example, each linking member preferably extends in a direction which, in use, will be substantially horizontal. The linking members of different frame units are suitably located at different heights, so that they do not contact one another.

The first and second frame members of each frame unit suitable extend generally vertically, or at an angle to the vertical, for example at an angle between 0 and 45° more preferably between 0 and 30° to the vertical. Preferably, the first and second frame members extend towards one another in the direction extending from the floor contacting part. The first and second rostrum support points are preferably located closer to one another than the respective floor contacting parts of the first frame member and second frame member.

The floor contacting part of each frame member may be of any suitable form. For example, it may comprise a simple foot. However, the floor contacting part preferably comprises a structure for travelling over a floor surface, for example a sliding surface (such as a skid), wheel or roller.

Each frame member preferably extends up to and no further than the respective rostrum support point, in order to avoid the presence of upwardly extending members above the respective deck. However, in some cases, a respective frame member may extend beyond the respective rostrum support point to provide a support, for example, for a handrail or side guard.

The first and second trusses extend from the respective frame member. Preferably, the first and second truss extend in a generally vertical direction or at a direction inclined to the vertical. Preferably, the respective trusses extend at an angle which is in the range 0-60°, preferably 0.45° to the vertical. The first and second trusses preferably extend towards one another in the direction away from the respective frame members. As a result, each respective frame unit resembles the form of a M. However, where there is a linking member, the first and second trusses preferably extend from the respective frame member to the linking member and do not meet one another. Preferably, the first and second truss extend from the respective first or second rostrum support point.

Preferably, there is no floor contacting part between the floor contacting part of the first frame member and the floor contacting part of the second frame member. This allows the structure to roll smoothly over a floor surface, allowing for any unevenness between the respective ends of the support structure, and simplifies construction.

Where is a linking member, the first and second trusses of different frame units meet the respective linking member at different positions, to allow the respective frame units to retract and nest together smoothly.

Preferably, the first frame member, first truss and linking member together define a triangulated structure, which gives rigidity. Similarly, the second frame member, second truss and the linking member preferably form a second triangulated structure for rigidity. Preferably, the first triangulated structure and second triangulated structure are separated from one another by a length of the linking member.

It is found that this space between respective triangulated structures provides a useful space within which other structures, such as the latch of the second aspect of the invention, may conveniently be located.

Where there is a linking member, the frame unit resembles something like a M with a line across the middle which preferably truncates the lower part of the middle triangle of the M.

In an alternative embodiment, the first and second trusses extend between the first frame member and the second frame member or between the second frame member and the first frame member, respectively forming a structure resembling a X between two uprights (which may also be thought of as the M or D rune of the futhark runic alphabet as commonly accepted).

If the trusses are then connected where they cross, two triangulated structures can be provided, for added rigidity. A linking member may additionally be provided as well, to provide further rigidity.

At least one, or each frame unit preferably comprises at least one foot extending from the floor contacting part of a respective frame member, for maintaining the respective frame unit in an upright position. The foot preferably extends in a direction substantially parallel to the retraction direction. Each foot of each frame unit may be nestable and retractable adjacent the respective foot of an adjacent frame unit. Preferably, each frame unit comprises a foot extending from each of the floor contacting part of the first frame member and the second frame member. Preferably, the feet of a smaller frame unit are located between the feet of a larger frame unit, in the retracted position. Wheels may be provided at at least one end, and preferably at both ends of respective feet to aid sliding over a floor structure.

Stop means may be provided to control movement of a respective frame unit with respect to a larger or smaller frame unit. A stop means may comprise a latch means for fixing the frame units in the extended position. Preferably, the latch or stop comprises a latch according to the second aspect of the invention.

A support member may be provided extending from a respective rostrum support point, for supporting a deck. Suitably, the support member extends from the respective frame unit in a cantilever fashion. Preferably, the support member extends in a direction which, in use, is substantially horizontal. Preferably, a support member extends from each rostrum support point. Respective support members of adjacent frame units are preferably configured so that they do not prevent retraction of a smaller frame unit into a larger frame unit.

Each support member may be independently adjustable in height and/or angle with respect to the frame unit from which it extends, so that a deck supported by it can be made level. Preferably, a support member comprises a contact member for contacting a deck or a frame unit located immediately below the frame unit to which the support member is attached. In this way, an improved support of weight applied to the deck on the support member can be obtained. Means may be provided to enhance sliding between a support member and the deck or frame unit of an adjacent frame unit. For example, sliding surfaces or a roller may be provided. A roller may be provided on the underside of the support member or on the top of the respective frame unit. Preferably, each rostrum support point comprises a bracket, the bracket comprising a sliding surface or roller, over which a support member of another frame unit may slide or roll and a support point for adjustably supporting the respective support member. The bracket may also comprise a mounting member, for supporting a riser. A riser comprises a substantially vertical surface extending between adjacent decks, to close the space between the adjacent decks.

In the rostrum of the first aspect of the invention, there are at least two frame units, each supporting a respective deck. Each deck may be constructed from known materials, in a known fashion. Because the frame units of the present invention are rigid in their own right, the design or plan of the decks is not restricted. In an embodiment of the invention, at least one deck has at least one curved edge when seen in plan. Preferably, all decks have at least one curved edge. Preferably, both front and back edges are curved. Preferably, each deck defines a section of arc. In this way, a curved rostrum can be assembled. The rostrum units are preferably movable in a direction substantially parallel to the radial direction of the section of arc at the centre of the deck.

Each frame unit, truss, linking member or other structure may be formed of any suitable structure as will be known to the person skilled in the art. For example, they may independently comprise tubes, girders, I beams, T-section beams, solid beams or any other suitable structural unit. They may be made of any suitable material, for example wood or metal. Preferably, they are formed of steel or aluminium.

Each support structure may be completed, assembled and designed off site and be brought to the location in which the rostrum is to be assembled, more easily than conventional nested system, because each support structure is modular.

In the rostrum structure of the second aspect of the invention, there is at least a first rostrum unit and a second rostrum unit. Each rostrum unit may comprise a support structure and a deck. The support structure may be according to the first aspect of the invention. Alternatively, it may be an A frame as described in WO2008/149077.

However, the second rostrum unit must be movable in a retraction direction between an extended position and a position in which it is retracted into the first rostrum unit.

The latch of the second aspect of the invention comprises a movable member which is mounted on one of the first and second rostrum units. The movable member may be movable by any suitable means. For example, it may be slidably mounted or it may be rotatably mounted.

The movable member is preferably movable into and out of engagement with the latch surface in a direction which is substantially parallel to the planes of the decks in the sense that the angle between its direction of motion and the plane of the deck nearest to it is less than 30°, more preferably less than 20° and preferably less than 10°. The movable member is preferably movable into and out of engagement with the latch surface in a direction which is substantially normal to the retraction direction, in the sense that the angle between them is more than 60°, preferably more than 70° and preferably more than 80°.

Preferably, the movable member comprises means for biasing the movable member into a selected position. Suitably, it is biased into a position in which it engages with a respective latch surface.

The movable member may be biased by any suitable means, for example by a spring or by a weight. It is particularly preferred that the movable member comprises a rotatably mounted unit, mounted for rotation about an axis which is not vertical and is preferably substantially horizontal, a weight being provided to bias the movable member into a selected position. Suitably, the weight is located on the opposite side of a fulcrum to the part of the movable member which is for engaging the latch surface.

The latch surface is mounted on the other of the first and second rostrum units and it is configured so that the movable member can engage the latch surface. Engagement of the latch surface and movable member is such that, when engaged, respective movement in at least one of the retraction direction and an opposed, extending direction is prevented and preferably movement in both the retraction direction and extending direction is prevented. In the latter case, there is preferably a second latch surface opposed to the first latch surface between which latch surfaces the movable member is received.

The movable member is preferably located under the deck of the rostrum unit on which it is mounted. The latch surface is preferably located under the deck of the rostrum unit on which it is mounted.

In a preferred embodiment, a second latch is provided for fixing the second rostrum unit with respect to the first rostrum unit in the retracted position. The second latch may comprise at least one of the latch surface and the movable member of the first latch.

In a preferred embodiment, the movable member is mounted on the second rostrum unit. As such, it should be mounted on part of the second rostrum unit which is adjacent to the first rostrum unit, in the extended position. In this case, the latch surface is provided at a part of the first rostrum unit which is adjacent the second rostrum unit in the extended position.

In a particularly preferred embodiment, the movable member is mounted in a structure comprising an abutment surface, the abutment surface being configured so that, when the movable member is engaged with the latch surface on the other of the first and second rostrum units, it is also engaged with the abutment surface. This has the advantage that support for the movable member, to ensure strong reliable locking, can be provided by the abutment surface rather than arranging for the forces to be resisted solely by the pivot or sliding surfaces of the movable member. Preferably, the abutment member comprises a slot into which the movable member is movable. The movable member should be movable into the slot in the direction which is parallel to the planes of the decks and substantially normal to the retraction direction.

In a preferred embodiment, there are at least three rostrum units, including a first, upper rostrum unit, a second, intermediate rostrum unit and a third, lower rostrum unit, each of the second and third rostrum units comprising a movable member and the first and second rostrum units each comprising a latch surface, the movable members of the first and second rostrum units being mounted on a structure comprising an abutment surface which the movable member contacts when the movable member is engaged with the respective latch surface.

In a preferred embodiment, a cam surface is provided on whichever of the first and second rostrum units comprises the latch surface, the cam surface being configured so that, as the movable member, moving with the respective rostrum unit, approaches the cam surface, it moves smoothly over the cam surface, against biasing means, the movable member moving into engagement with the latch surface, under the influence of the biasing means, when it comes out of engagement with the cam surface.

Preferably, means are provided for moving a respective movable member only if engaging with a latch surface. For example, manually operated, mechanically operated or powered means may be provided for moving the movable member out of engagement with the latch surface, to allow the rostrum units to be moved with respect to one another.

Preferably, there is a first, upper rostrum unit, a second, intermediate rostrum unit and at least a third, lower rostrum unit, a movable member being provided on one of the first and second rostrum units and a latch surface being provided on the other of the first and second rostrum units, an unlatching cam surface being provided on the third rostrum unit, arranged so that, as the third rostrum unit is moved into a retracted position with respect to the second rostrum unit, the unlatching cam surface engages the movable member so that it moves it out of engagement with the latch surface. In this way, once the first rostrum unit is moving, it can be used to automatically unlatch the second rostrum unit so that the second and third rostrum units can both be moved into their respective retracted positions.

The same principle can apply to a series comprising 3, 4 or more rostrum units.

A manually operated latch may be provided for the third rostrum unit. In this way, only one manual unlatching operation has to be carried out, the entire set of rostrum units then being unlatched ready for movement.

Abutment surfaces may be provided between parts of the third rostrum unit and the second rostrum unit which are adjacent to one another when the third rostrum unit is in the retracted position with respect to the second rostrum unit. In this way, a force applied to the third rostrum unit can be transferred to the second rostrum unit, allowing the second rostrum unit to be driven into its retracted position.

In a preferred embodiment, the unlatching cam surface is part of the same structure as at least one of (and preferably both of) the movable member and abutment surface.

The present invention will be further described by way of example only with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear view of a rostrum according to a first aspect of the invention.

FIG. 2 is a schematic side view of a rostrum according to FIG. 1, in an extended position.

FIG. 3 is a schematic side view of a rostrum according to FIG. 1, in a retracted position.

FIG. 4 is a sketch plan view of a rostrum according to the second aspect of the invention showing the positions of movable members and latching surfaces.

FIG. 5 is a sketch isometric view of a first latch component of the second aspect of the invention.

FIG. 6 a is a sketch plan view of a latching mechanism for use with the second aspect of the invention.

FIG. 6 is a sketch plan view of a latching mechanism for use with the second aspect of the invention, as rostrum units are moved together.

FIG. 7 is a sketch rear view corresponding to FIG. 6.

FIG. 8 is a sketch plan view of a latching mechanism for use with the second aspect of the invention, with the movable member engaged with a latching surface.

FIG. 9 is a sketch rear view corresponding to FIG. 8.

FIG. 10 is a sketch plan view of the latching mechanism for use with the second aspect of the invention, being unlatched.

FIG. 11 is a sketch rear view corresponding to FIG. 10.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in rear view, a rostrum according to the first aspect of the invention, comprising a rostrum support structure according to the first aspect of the invention, the rostrum support structure comprising a first frame unit 10, a second frame unit 20, a third frame unit 30, a fourth frame unit 40, a fifth frame unit 50.

The first frame unit 10 comprises a first frame member 11 which extends from a floor contacting part 12 (here shown incorporating a roller 13), to a first rostrum support point 14 which will be explained further below.

A first truss 15 extends from the first frame member 11 at the first rostrum support point 14. The first frame member is inclined generally inwards in the upward direction whereas the first truss 15 extends away from the first frame member 11 in the downward direction. A linking member 16 is provided which is connected to both the first frame member 11 and the first truss 15 to form a triangulated structure. A corresponding construction is formed on the opposite side of the frame unit (which in this case is symmetrical, though it need not be so). In particular, there is a second frame member 17 and a second truss 18. The second frame member 17 and the second truss 18 are linked by the same linking member 16 to form a triangulated structure. The resulting frame unit is strong and rigid, allowing safe support of loads applied to deck of the rostrum, supported at the rostrum support point.

It can be seen that the first and second trusses 15 and 18 meet the linking member 16 at points which are displaced from one another 19 by a small distance.

A similar structure appears in each of the successive frame units 20, 30, 40 and 50. For example, the second frame unit comprises a first frame member 21 and a first truss 25, linked by a linking member 26 to form a triangulated structure. There is a second frame member 27 and a second truss 28 also linked by the linking member 26 to form a triangulated structure. The first truss 25 and the second truss 28 meet the linking member at points 29 which are displaced from one another and displaced from one another by a greater distance than the respective points 19 of the first frame unit.

It can be seen that the resulting second frame unit 20 can be contained entirely within and below the structure of the first frame unit 10. A corresponding arrangement is repeated so that all of the frame units are stackable together, with the fifth frame unit 50 inside the fourth frame unit 40 which is inside the third frame unit 30 which is inside the second frame 20 which is inside the first frame unit 10. The frame members and trusses of each frame unit lie in the same, generally vertical plane. The linking members 16, 26, 36, 46 and 56 are configured so that, in the retracted position, they lie adjacent to one another and positioned so as not to prevent stacking of the frame units.

The first frame unit 10 supports a first deck 71, the second, third, fourth and fifth frame units 20-50 supporting respective decks 72, 73, 74 and 75.

As shown in FIG. 2, which is a schematic view of the rostrum of FIG. 1, seen from the left, in an extended position, each rostrum unit comprises a respective frame unit, of which the first frame member 11, 21, 31, 41 and 51, in each case is visible. Each frame unit includes a respective foot, 81, 82, 83, 84, 85, which extends generally parallel to the floor surface, rigidly attached to the respective first frame member 11, 21, 31, 41, 51.

Floor rollers 13, 23, 24, 25, 26 at the floor contacting part of each first frame member can be seen. A further roller is provided at the outward end of each foot, of which the outward roller 13 a of the first frame unit 10 can be seen in FIG. 3 and the roller 26 a of the fifth frame unit can be seen in FIG. 2. Each rostrum unit comprises a respective deck 71, 72, 73, 74 and 75, supported by a corresponding support member 81, 82, 83, 84 and 85. The second to fifth rostrum units each comprise a bracket 86, 87, 88 and 89 respectively mounted at the top of the respective first frame member 21, 31, 41 and 51. Each of these brackets comprises a roller 76, over which the respective support member of a rostrum unit immediately above the bracket can roll during retraction/extension, and an adjustable mounting 77 which allows the height and/or angle of the support member to be varied with respect to the corresponding rostrum support point so that the deck can be made level. A riser 78 is fixed to the front of the bracket 86, so that the rostrum presents a substantially closed structure, preventing objects from being lost inside the structure of the rostrum when in use.

FIG. 4 is a sketch plan view of a rostrum structure according to the second aspect of the invention. It comprises three rostrum units, of which the respective decks 101, 102 and 103 can be seen. In this embodiment, deck 101 is the highest, followed by deck 102 with deck 103 being the lowest.

Each rostrum unit will comprise a rostrum support structure which is preferably according to the first aspect of the invention and as shown in FIG. 1. Details are not shown, except that the approximate positions of support members 104 are shown schematically. FIG. 4 is shown with the edge of the rostrum which will be at the front at the top of the drawing. The second rostrum unit 102 can be retracted and nested inside the first rostrum unit 101 and the third rostrum unit 103 can be retracted and nested inside the second rostrum unit 102. Two latching mechanisms are shown. Each latching mechanism comprises a first latching component 105 which extends from the rear of a lower rostrum unit, for example 103, 102. Each of the first components 105 comprises a movable member 106, of which the top is visible in FIG. 4, sitting in a slot 107 of the respective component 105. A second latching component 108 is shown, which is fixed on the rostrum unit which is located above the rostrum unit with the respective first component 105. The second latching component 108 comprises a cam surface 109 (as can be seen in FIG. 6) and a latching surface 110.

FIG. 5 is a sketch isometric drawing of the first latching component 105 which is used in each case. The movable member 106 is shown, pivotally mounted at a pivot 111. It is biased into an upright position by a weight 112 at its bottom end, so that its top end 113 engages in a slot 107. A second cam surface 114 is provided, the function of which will be described further below.

In a starting position, with the respective rostrum units nested inside one another, in the position as shown in FIG. 6 a, the second latching component 108 of the first rostrum lies substantially in front of the first latching component 105 of the second rostrum unit. As the second rostrum unit 102 is rolled forwards (towards the top of the page), the first latching component 105 approaches the cam surface 109 of the second latching component as shown by the dotted arrow.

As a result, as shown in FIG. 6, the top end 113 of the movable member 106 slides along the cam surface 109 in the direction shown by the solid arrow in FIG. 6, rotating about the pivot 111. As the second rostrum unit moves to its maximum, extended position, the top end 113 of the movable member 106 rides over the end of the cam surface 109. As a result, it engages with the latching surface 110 of the second latching component 108. In this position, movement of the second rostrum unit in the retracting direction is prevented by engagement of the movable member 106 with the latching surface 110. In this position, the top end 113 of the movable member 106 is held in a slot 107 in the first latching component 105. In practice, there would be a tighter fit than is shown in FIG. 6 etc., so that rigid support is given to the top end 113 of the movable member 106. If an attempt is made to move the second rostrum unit 102, this movement is resisted by the walls of the slot 107 and the latching surface 110 which are relatively close together and can be made relatively strong, so that the forces are not taken by the pivot 111, so that the pivot 111 can be made of a relatively simple design.

The sequence of movements whereby the third rostrum unit 103 is moved into the extended position with respect the second rostrum unit 102 and latched in position is exactly the same.

When it is desired to retract the rostrum units, in a first step, an operator actively unlatches the movable member 106 of the third rostrum unit 103. This may be achieved by any suitable mechanism. For example, an operator may be simply reach their hand in to move the top end 113 of the movable member 106 out of engagement with the latching surface 110. Alternatively, an operating device, for example a cable, string, rod or the like may be provided for operating the movable member. A locking mechanism may be provided so that only an operator in possession of a suitable key or code word can unlock the third rostrum unit. An electrically powered unlocking mechanism may be provided for this rostrum unit. Once the third rostrum unit is unlatched and caused to move in the retracting direction, the first latching component 105 a of the third rostrum unit 103 moves towards the first latching component 105 of the second rostrum unit which is engaged with the second latching component 108 of the first rostrum unit. This is shown by the dotted arrow in FIG. 10. As a result, the second cam surface 114 a of the first latching component 105 a of the third rostrum unit 103 engages the lower end of the movable component 106, causing the movable member 106 to rotate as shown by the solid arrows in FIG. 11, in a clockwise direction. As a result, the top end 113 of the movable member is moved out of engagement with the latching surface 110.

A drive means is provided, whereby when the rostrum unit 103 is in the retracted position with respect to the second rostrum unit 102, a force applied to the third rostrum unit is transmitted to the second rostrum unit 102. The relative position of the first latching component 105 a of the third rostrum unit with respect to the first latching component 105 of the second rostrum unit is designed so that unlocking of the movable member 106 occurs just before the third rostrum unit 103 enters its fully retracted position so that the second rostrum unit 102 becomes movable at that point.

The present invention has been described above by way of example only and modifications can be made within the invention. The invention also consists in any individual features described or implicit herein or any combination of any such features or any generalisation of any such features or combination. 

1. A support structure for a rostrum, comprising: a first frame unit and at least a second frame unit, retractable into the first frame unit, each frame unit comprising: a first frame member, extending from a floor contacting part to a first rostrum support point and a first truss extending from the first frame member, a second frame member, extending from a floor contacting part to a second rostrum support point and a second truss extending from the second frame member, wherein, in each frame unit: (c) there is a linking member, connecting the first and second frame members and first and second trusses, at points displaced from the first and second rostrum support points; or (d) the first and second trusses are connected to the second and first frame members respectively, at points displaced from the first and second rostrum support points.
 2. A rostrum support structure according to claim 1, wherein the first and second frame members and the first and second trusses lie in a first plane, there being a linking member located in a plane displaced from the first plane.
 3. A rostrum support structure according to claim 1, wherein the first and second rostrum support points are located closer to one another than the respective floor contacting parts of the first frame member and second frame member.
 4. A rostrum support structure according to claim 1, wherein, in a respective frame unit, the first and second trusses contact the linking member at points which are displaced from one another.
 5. A rostrum support structure according to claim 4, wherein, in different frame units, the first and second trusses contact the linking member at different points.
 6. A rostrum support structure according to claim 1, wherein the first frame member, first truss and linking member define a first triangulated structure and the second frame member, second truss and linking member form a second triangulated structure.
 7. A rostrum, comprising a plurality of decks supported by a plurality of rostrum support structures according to claim
 1. 8. A rostrum structure, comprising: a first rostrum unit and at least a second rostrum unit, wherein the second rostrum unit is movable in a retraction direction between an extended position and a position in which it is retracted into the first rostrum unit, each rostrum unit having a deck; a latch, for fixing the second rostrum unit with respect to the first rostrum unit in the extended position, the latch comprising a movable member, mounted on one of the first and second rostrum units, and a latch surface mounted on the other of the first and second rostrum units, with which the movable member engages to fix the second rostrum unit with respect to the first rostrum unit in the extended position, the movable member being movable into and out of engagement with the latch surface in a direction parallel to the planes of the decks and substantially normal to the retraction direction.
 9. A rostrum structure according to claim 8, wherein the movable member is rotatably mounted.
 10. A rostrum structure according to claim 8, wherein the movable member is biased into a position in which it engages with a latch surface.
 11. A rostrum structure according to claim 8, wherein the movable member is biased into engagement with the latching surface by a weight.
 12. A rostrum structure according to claim 8, wherein movement in both the retraction direction and extending direction is prevented by engagement of the movable member with the latch surface.
 13. A rostrum structure according to claim 12, further comprising a second latch surface opposed to the first latching surface, the movable member being received between the first and second latch surfaces.
 14. A rostrum structure according to claim 8, wherein a cam surface is provided on whichever of the first and second rostrum units comprises the latch surface, the cam surface being configured so that, as the movable member, moving with the respective rostrum unit, approaches the cam surface, it moves over the cam surface against biasing means, the movable member moving into engagement with the latch surface under the influence of the biasing means, when it comes out of engagement with the cam surface.
 15. A rostrum structure according to claim 8, wherein means are provided for moving a respective movable member out of engagement with a latch surface.
 16. A rostrum structure according to claim 8, comprising a first, upper rostrum unit, a second, intermediate rostrum unit and a third, lower rostrum unit, a movable member being provided on one of the first and second rostrum units and a latch surface being provided on the other of the first and second rostrum units, an unlatching cam surface being provided on the third rostrum unit, arranged so that, as the third rostrum unit is moved into a retracted position with respect to the second rostrum unit, the unlatching cam surface engages the movable member so that it moves out of engagement with the latch surface. 17-18. (canceled) 